A group of vertebrate animals that have an amnion, a protective membrane around the embryo, including reptiles, birds, and mammals.
From Greek 'amnion' (lamb's caul, membrane around fetus) plus the Latin plural suffix '-otes'. The term was coined in the early 20th century to classify vertebrates based on this shared embryological feature.
Amniotes were a crucial evolutionary innovation—this membrane allowed vertebrates to reproduce fully on land without needing water, which is why you'll find amniotes everywhere from deserts to mountains, but amphibians (without the amnion) must stay near water to breed.
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